1. Field of the Invention
The present invention relates to a system for systematically recording data corresponding to selected machine parameters over time and for downloading and analyzing that data once it has been recorded. More particularly, the present invention relates to a system for recording and analyzing vehicle data.
2. The Prior Art
It is often desirable to record information pertaining to the operation of a machine, particularly a vehicle, over time. This information is useful in analyzing both the operating condition of the machine and how the machine is being controlled by the operator during the monitoring period. Also, this information can be useful in determining the condition of a machine just prior to, or just after, a specific incident or event (such as engine overheating, brake failure, a vehicle accident, or the like) for maintenance, insurance, or legal purposes.
Various systems to monitor and record vehicle data have been provided in the prior art. Many of these systems provide onboard devices that record the data for a period of time and then transfer the data to a remote location for later analysis. U.S. Pat. No. 5,046,007, to McCrery et al., and U.S. Pat. No. 5,065,321, to Bezos et al., provide examples of this type of system. While it is desirable to record many different data signals for a long period of time, memory concerns limit the amount of data which may be stored in an on-board device.
Rather than storing the data from each sensor in real time, a system can be more efficient if it provides a means for compressing the data by storing only portions of the sensed data, while ensuring that at least the most relevant information is stored. With such compression, a given amount of memory can store data covering a much longer period of time.
Various prior art systems provide for compressing vehicle data as the systems record such data. U.S. Pat. Nos. 5,327,347, to Hagenbuch, and 4,258,421, to Juhasz et al., which are herein incorporated by reference, are representative of microprocessor-based digital systems that compress data by sampling a plurality of sensors at a particular frequency and storing the data provided by the sensors only when they are sampled. The Juhasz et al. patent discloses a system that further compresses the data by comparing each data signal with a reference threshold and only storing the data signal if the data signal exceeds its reference threshold.
While these type of systems increase the period of time the system is capable of recording data, it is also possible for an incident or event to occur during the time between samples. The data surrounding this incident can be extremely important. Thus, while decreasing the sampling rate or frequency increases the operating time that may be recorded in a memory of a particular capacity, it also decreases the likelihood that a sample will be taken at, or around, the time of an incident. Of course, the inverse of this is also true: increasing the sampling frequency decreases the operating time that may be recorded, but it increases the likelihood that a sample will be taken at, or around, the time of an incident.
Further, even if a sample is taken at the time of an incident, if the sample frequency is too low, important information before and after the incident may be missed. Thus, while normal operating data can be useful if stored at a low frequency, data surrounding the time of an incident is most useful if it is stored at a high frequency so that better resolution is provided for analysis.
U.S. Pat. No. 4,638,289, to Zottnik, discloses a system that records vehicle data just prior to an accident. The Zottnik patent provides for periodically sampling a plurality of sensors at a relatively high frequency and stores the record created by each sampling in memory. Once a predetermined number of records are stored, the next record is stored over the oldest record. Thus, the memory always contains a predetermined number of the most recent records. Upon sensing an accident, the system freezes the data stored in memory, for later analysis. Because the system only retains the data immediately preceding an accident, a high sampling frequency may be used without encountering memory concerns.
A further problem that exists with the prior art monitoring and recording systems occurs when a particular system provides for sampling a large number of sensors. There are difficulties associated with installing the system in a vehicle if the installer has to connect each sensor to one predetermined input channel on the device. This procedure requires that the installer carefully match each input sensor to the predetermined input channel associated with that sensor and further requires that the input channel labels be determined prior to installation.